The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Fiber is an optimal medium for transmitting signals. A strand of fiber is capable of carrying an enormous amount of information using light waves of multiple wavelengths. Under Wavelength Division Multiplexing (WDM), each of the multiple wavelengths transmitted in the strand of fiber can be an independent carrier for a client signal. The client signal thus carried may be any type such as Ethernet frames, IP packets, a fiber channel signal, a SONET or SDH signal, etc.
Because signals transmitting through a fiber experience relatively lower loss than signals transmitting through many other types of media, fiber nowadays is a medium of choice for both long-haul and short-haul transport networks. As a result, optical fibers have been widely deployed. This trend of deployment of optical fibers will most likely continue for a foreseeable future.
Fiber is a very secure medium. First, fibers are typically buried, submerged, or otherwise in places thought to be difficult for intruders to access. Second, to tap into an optical signal, a fiber that carries the signal would typically have to be cut. Such a fiber cut would cause instantaneous interruption to a large number of communication channels, including but not limited to those directly carried by the fiber. A system that monitors any of these large number of communication channels could easily detect and report losses of signal and raise critical alarms. Responding to the alarms, technicians could use tools to isolate the location of the fiber cut, thereby thwarting the malicious attempt to intercept the optical signal carried in the fiber.
However, it is not difficult for a relatively motivated intruder to find access to signal-carrying fibers, especially in light of their wide deployment. Furthermore, prompt and precise isolation of a fiber cut is by no means simple to accomplish. For example, deploying monitoring systems and assigning monitoring in large networks add strains to typically already expensive operating budgets of communications carriers. Therefore, not all fibers may be so closely monitored; a large number of fiber deployments may be left not as secure as one would like them to be.
In addition, it is now technologically feasible for intruders to install clip-on tapping devices on fibers without cutting the fibers. Therefore, no loss of signal might be detected because signal transmission in the fibers would not be interrupted. Even though new, expensive, monitoring systems can theoretically be deployed to detect signal attenuation caused by the tapping devices, still some sophisticated tapping devices may cause too little signal attenuation to be effectively detected, located, and stopped. As a result, even where there is no fiber cut, optical signal transmission may not be as secure as one would imagine it to be.